1. Field of the Invention
The present invention relates to a leakage measuring device for measuring a leakage rate of a circuit or the like which constitutes a measuring object.
2. Description of the Prior Art
As a measuring device for the above purpose, a measuring device shown in FIG. 6 has been known conventionally.
This conventional measuring device incorporates a piston 2 in a cylinder 1 slidably and divides the inside of the cylinder 1 into one pressure chamber 3 and the other pressure chamber 4.
A piston rod 5 is mounted on a side surface of the piston 2 which faces the other pressure chamber 4 and this piston rod 5 is protruded outwardly from the cylinder 1.
A rack member 6 is provided to a distal end of the piston rod 5 and a rack 6a formed on the rack member 6 is meshed with a pinion 8 of an encoder 7. Accordingly, when the piston 2 is moved, the pinion 8 is rotated and a digital signal in response to the movement of the piston 2 is outputted from the encoder 7.
In the drawing, numeral 9 indicates a seal member provided around the periphery of the piston 2 for preventing a leakage between both chambers 3, 4, while numeral 10 indicates a seal member for sealing the periphery of the piston rod 5.
In an actual use of the measuring device having the above-mentioned construction, for example, one pressure chamber 3 is connected to a pressurizer not shown in the drawing and the other chamber is connected to a circuit or the like which constitutes a measuring object or an object to be measured.
When pressure is applied to one pressure chamber 3, if there is no leakage at the measuring object side, the piston 2 is not moved. However, if there is a leakage at the measuring object side, the piston 2 is moved. Accordingly, the movement of the piston 2 is proportional to the leakage at the measuring object side. Then, the movement of the piston 2 is measured by the encoder 7 so as to measure the leakage at the measuring object side.
In case the leakage rate at the measuring object side is zero and the piston 2 is stopped at a fixed position, the pressure generated in the other pressure chamber 4 is higher than the pressure generated in one pressure chamber 3. It is because that the pressure receiving area of the piston 2 in the other pressure chamber 4 is smaller than the pressure receiving area of the piston 2 in one pressure chamber 3 by the cross-sectional area of the piston rod 5.
Because of the presence of the pressure difference between these pressure chambers 3, 4, the measuring device must be provided with the seal member 9 around the periphery of the piston 2. It is because that the greater the pressure difference between these chambers 3, 4, the leakage from the high pressure side to the low pressure side is increased.
Furthermore, in proportion to the increase of the pressure in the other pressure chamber 4, the necessity of the seal member 10 is increased.
Besides the measuring device shown in FIG. 6, a measuring device shown in FIG. 7 has been also known conventionally.
The measuring device shown in FIG. 7 incorporates a piston 12 in a large diameter cylinder 11 and defines a pressurizing chamber 13. Air pressure is introduced into this pressuring chamber 13 by means of a pressurizer not shown in the drawing.
A plunger 14 is provided to a side surface of the piston 12 which is opposite to the pressurizing chamber 13. The plunger 14 has a distal portion thereof slidably incorporated in a small diameter cylinder 15 which is formed contiguously with the large diameter cylinder 11. A measuring pressure chamber 16 formed in the small diameter cylinder 15 is connected with a circuit which constitutes a measuring object.
The piston 12 is provided with a scale indication rod 17 and this scale indication rod 17 is protruded outwardly from the large diameter cylinder 11 in parallel with the small diameter cylinder 15. On the outside of the small diameter cylinder 15, a scale 18 is marked and this scale 18 and the scale indication rod 17 face with each other in an opposing manner as shown in the drawing.
In the drawing, numeral 19 indicates a drain chamber and numerals 20, 21 indicate seal members.
The measuring device having the above-mentioned construction adopts an operation principle similar to that of the measuring device shown in FIG. 6. Namely, when air pressure is supplied to the pressurizing chamber 13, the piston 12 is stopped at a position where the piston 12 is balanced with a pressure action of the measuring pressure chamber 16. Then, when an oil leakage occurs at the circuit side which constitutes the measuring object, the piston 12 is moved and this movement can be inspected visually in view of the correspondence between the scale indication rod 17 and the scale 18. Based on the movement of the piston 12 detected in this manner, the leakage at the measuring object side can be measured.
The measuring device shown in FIG. 6 has following problems.
Namely, as the pressure difference between both pressure chambers 3, 4 becomes large, the leakage from the other pressure chamber 4 which is at a high pressure to one pressure chamber 3 which is at a low pressure occurs.
When the leakage occurs between both pressure chambers 3, 4, it becomes difficult to determine whether the movement of the piston 2 is caused by a leakage at the measuring object side or the internal leakage of the measuring device per se. Accordingly, the leakage at the measuring object side cannot be measured accurately.
As means for preventing such a leakage, it is considered to increase an interference of the seal member 9. When the interference of the seal member 9 is increased, however, the piston 2 cannot enjoy the smooth movement and a so-called stick-slip phenomenon occurs. Accordingly, the measured value outputted from the measuring device is vigorously fluctuated resulting in the inaccurate measurement of the leakage.
Furthermore, even in case the interference is not increased, the seal members 9, 10 are deformed when they are respectively subjected to a high pressure and hence, the friction of the seal members 9, 10 is increased. In this manner, in case the friction of the seal members 9, 10 is increased during the measuring process, the relative relation between the pressure action of one pressure chamber 3 and the movement of the piston 2 cannot be fixed. In this case, the leakage cannot be measured accurately also.
The measuring device shown in FIG. 7 also has a problem that it cannot avoid adverse effects caused by the seal members 20, 21 and it is considerably difficult to inspect the movement of the piston 12 visually.
In any case, the above-mentioned conventional measuring devices have a problem that it cannot measure the leakage easily and accurately due to the interaction among various factors.
Accordingly, it is an object of the present invention to provide a leakage measuring device capable of always performing the accurate measurement of the leakage.